1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing devices and, more particularly, to a measuring device for use in a plasma reactor.
2. Prior Art
In the manufacture of semiconductor integrated circuit devices, various circuit elements are formed in or on a base substrate, such as a silicon substrate. Various processes for forming these integrated circuit devices are well known in the prior art. In performing some of these steps, a semiconductor wafer is placed in a reactor chamber in order for the wafer to undergo certain necessary processing steps, which may include steps for depositing or etching various layers of the wafer. When these wafers are loaded into a given chamber, the wafer is placed on a wafer chuck, which is a type of semiconductor platen. These platens, or chucks are used to control the wafer temperature during a given process cycle. In most of these processes it is desirable that the energy input into the wafer is known in order to control the various process parameters.
In order to control the amount of energy coupled to the wafer, various prior art schemes have been devised to measure the energy flux in the reactor chamber. These prior art techniques include, for example, directly monitoring an electrical circuit parameter, such as an RF bias voltage; and indirect methods such as the use of temperature measuring probes within the chamber. Although a number of prior art monitoring schemes are available, these methods may not necessarily provide accurate assessment of the amount of energy coupled to the wafer itself. This is notably so in processing systems where plasma is utilized in the reactor chamber for processing the wafer.
In many prior art plasma systems, indirect methods are utilized to measure the energy flux to the wafer. Typically, in these instances, a circuit parameter, such as the RF bias voltage, is monitored to calculate (or extrapolate) the energy flux based on the specifications provided for the given reactor. Direct measurements can provide more accurate and continuous results, but are difficult to obtain. For example, direct measurements by the use of probes within the chamber are not desirable, because such probes are intrusive and tend to interfere with the plasma field. That is, the intrusive probe may interact with the plasma field, thereby altering the flux field and/or density of the plasma field. Additionally, isolation of such probes is difficult to achieve and noise induced can contribute to erroneous readings.
Furthermore, although some of these prior art energy monitoring techniques may provide an accurate measurement of energy flux in the reactor chamber, such measurements may not reflect the actual flux to the wafer. In practice, it is desirable to know the actual value of the energy flux to the wafer and not necessarily the energy flux in the reactor chamber as a whole.
Accordingly, it is appreciated that what is needed is an energy monitoring technique in which the energy coupled to the wafer is measured accurately, but without interfering with the plasma field in the reactor chamber.